JP4909878B2 - Disk drive device and clearance adjustment method thereof - Google Patents

Description

  The present invention relates to a disk drive device and a clearance adjustment method thereof, and more particularly to a clearance adjustment technique suitable for a disk drive device that does not have a barometric pressure sensor.

  As a disk drive device, a device using a disk of various modes such as an optical disk, a magneto-optical disk, or a flexible magnetic disk is known. Among them, a hard disk drive (HDD) is a computer storage device. As one of the storage devices indispensable in the present computer system, it is widely used. In addition to the computer, the use of the HDD such as a moving image recording / reproducing apparatus, a car navigation system, or a mobile phone is increasing more and more due to its excellent characteristics.

  A magnetic disk used in an HDD has a plurality of data tracks and servo tracks formed concentrically. Each servo track is composed of a plurality of servo data having address information. Each data track is recorded with a plurality of data sectors including user data. Data sectors are recorded between servo data spaced apart in the circumferential direction. The head element part of the head slider supported by the oscillating actuator accesses the desired data sector according to the servo data address information, thereby writing data to the data sector and reading data from the data sector. It can be performed.

  In order to improve the recording density of the magnetic disk, it is important to reduce the clearance (flying height) between the head element portion that floats on the magnetic disk and the magnetic disk and changes thereof. For this reason, several mechanisms for adjusting the clearance have been proposed. One of them includes a heater in the head slider, and the clearance is adjusted by heating the head element portion with the heater (see, for example, Patent Document 1). In this specification, this is called TFC (Thermal Flyheight Control). The TFC supplies a current to the heater to generate heat, and causes the head element portion to protrude by thermal expansion. As a result, the clearance between the magnetic disk and the head element portion is reduced. In addition, a mechanism for adjusting the clearance between the head element portion and the magnetic disk using a piezo element is known.

The clearance changes in accordance with a change in temperature, and also changes in accordance with a change in atmospheric pressure (altitude) (see, for example, Patent Document 2). When the clearance setting value in read / write is 5 nm or more, the clearance change due to the altitude change can be dealt with by the clearance margin. However, when there is only a clearance of 2 or 3 nm or less in read / write, it is required to adjust the clearance according to a change in atmospheric pressure in addition to a change in temperature.
JP 2006-190454 A JP 2006-92709 A

  In a typical TFC, the heater power is increased in response to a decrease in temperature to cause the head element portion to protrude by thermal expansion, and compensates for an increase in clearance due to a decrease in temperature. On the other hand, when the altitude increases and the atmospheric pressure decreases, the flying height of the slider decreases. For this reason, the clearance between the head element portion and the magnetic disk also decreases due to the decrease in the atmospheric pressure. Therefore, if the temperature is constant, the TFC reduces the protrusion amount as the atmospheric pressure decreases.

  The HDD sets many parameters according to the temperature, and accurate temperature detection is indispensable for the normal operation of the HDD. Therefore, a general HDD has a temperature sensor as means for detecting temperature. Similarly, an atmospheric pressure sensor (altitude sensor) is known as one of means for detecting atmospheric pressure. However, the use of the pressure sensor increases the number of HDD members, and the cost of the HDD greatly increases. In addition, since there are almost no parameters to be set according to changes in atmospheric pressure other than parameters for adjusting the clearance, it is preferable to specify the atmospheric pressure without using an atmospheric pressure sensor.

  As described above, the clearance changes according to the change in atmospheric pressure. For this reason, a change in atmospheric pressure can be measured by referring to the clearance. Several techniques for identifying clearance are known. A typical method specifies a clearance (clearance change) from the amplitude of the read signal of the head element portion. As the clearance decreases, the signal strength increases and the gain of the variable gain amplifier decreases.

  Therefore, the signal strength and clearance can be specified by referring to the gain of the variable gain amplifier. A more accurate clearance specifying method specifies the clearance from the resolution (resolution) of the frequency component of the read signal. Alternatively, although the accuracy is inferior, the atmospheric pressure can be estimated from the current value of the spindle motor (SPM).

  In order to adjust the clearance according to the atmospheric pressure without using the atmospheric pressure sensor, refer to the HDD operating parameters (variable gain / amplifier gain, SPM current value, etc.) as in the above method, and change the clearance. It is necessary to specify. However, unlike a barometric sensor, the accuracy and reliability of barometric pressure measurement using HDD operating parameters is not high. Uncertain pressure measurement may cause incorrect clearance adjustment, causing head / disk contact and damaging the head slider or magnetic disk, or reading / writing without ensuring the necessary clearance margin. -Hard errors due to disk contact (errors that cannot be recovered) can be caused.

  A disk drive device according to an aspect of the present invention includes a head that accesses a disk, a moving mechanism that holds the head and moves the head on the disk, and adjusts a clearance between the head and the disk. An adjustment mechanism for controlling the temperature, a temperature sensor, and a controller for controlling at least the adjustment mechanism. The controller corrects the change amount due to the temperature change in the change amount from the default value of the operation parameter of the disk drive device using the detected temperature of the temperature sensor, and then changes the clearance according to the corrected change amount of the operation parameter. Determine the amount. Further, when the clearance change amount exceeds the reference range, the contact between the head and the disk is verified. Then, the adjustment amount of the clearance is determined based on the result of the verification of the contact. Thereby, the clearance adjustment according to atmospheric pressure can be performed more accurately without using an atmospheric pressure sensor.

  Preferably, the operation parameter is a parameter determined from an amplitude of a signal read from the disk by the head. Alternatively, the operation parameter is a parameter determined from a ratio of different frequency components of a signal read from the disk by the head. Thereby, the clearance change amount can be determined more accurately.

  The controller preferably controls the adjustment mechanism so that a clearance for verifying the contact is smaller than a default clearance corresponding to the determined amount of change in the clearance. As a result, an appropriate clearance including a clearance margin can be realized. Further, the controller preferably verifies the contact with a constant adjustment clearance amount by the adjustment mechanism. As a result, efficient processing can be performed, and performance degradation can be suppressed.

  It is preferable that the controller controls the adjustment mechanism so that the clearance is higher than the clearance set by default when the contact is confirmed in the contact verification. Thereby, the contact in a subsequent process can be prevented more reliably.

  In a preferred example, when the controller confirms contact in the contact verification, the controller sets the clearance higher than a clearance according to a default setting, and the amount by which the clearance is higher than the default setting determines the clearance in the contact verification. The adjustment mechanism is controlled to be the same as the amount to be made smaller than the default setting. As a result, an appropriate clearance including a clearance margin can be realized by efficient processing.

  Preferably, the controller changes a reference of the clearance change amount for determining whether or not to perform the contact verification based on the number of times the clearance change amount exceeds the reference range. Thereby, it is possible to perform an appropriate process according to the use environment. Preferably, the controller measures the change of the operation parameter a plurality of times, and determines whether the clearance change amount exceeds the reference range based on the measurement result of the plurality of times. Thereby, the clearance change amount can be determined more accurately.

  Another aspect of the present invention is a clearance adjustment method in a disk drive device. In this method, the temperature is detected by a temperature sensor. After the change amount due to the temperature change in the change amount from the default value of the operation parameter of the disk drive device is corrected using the detected temperature, the clearance change amount is determined based on the corrected change amount of the operation parameter. When the clearance change amount exceeds the reference range, the contact between the head and the disk is verified. The clearance adjustment amount is determined based on the result of the contact verification. Thereby, the clearance adjustment according to atmospheric pressure can be performed more accurately without using an atmospheric pressure sensor.

  According to the present invention, the clearance adjustment between the head and the disk according to the atmospheric pressure can be more accurately performed without using the atmospheric pressure sensor.

  Embodiments to which the present invention is applied will be described below. For clarity of explanation, the following description and drawings are omitted and simplified as appropriate. Moreover, in each drawing, the same code | symbol is attached | subjected to the same element and the duplication description is abbreviate | omitted as needed for clarification of description. In the following, embodiments of the present invention will be described by taking a hard disk drive (HDD) as an example of a disk drive device as an example.

  The HDD of this embodiment adjusts the clearance between a head element unit, which is an example of a head, and a magnetic disk, which is an example of a disk, by TFC (Thermal Fly height Control), which is an example of a clearance adjustment mechanism. The TFC adjusts the clearance by the thermal expansion of the head element portion due to the heat from the heater on the slider. The TFC of this embodiment adjusts the clearance according to changes in atmospheric pressure. The HDD has a temperature sensor but does not have an atmospheric pressure sensor.

  The HDD determines the clearance change from the change of the operation parameter. Furthermore, the temperature of the clearance change is corrected by correcting the operation parameter based on the temperature detected by the temperature sensor. Thus, the HDD determines a clearance change corresponding to the atmospheric pressure change, excluding the temperature change in the clearance change. The environmental conditions for changing the clearance include humidity in addition to temperature and atmospheric pressure, but the substantial change is due to temperature and atmospheric pressure. In the following, the clearance change after temperature correction is due to atmospheric pressure change. Will be described.

  The HDD of this embodiment verifies the contact between the head slider and the magnetic disk (head / disk contact) when the heater power is changed by TFC in accordance with the change in atmospheric pressure. Unlike a barometric sensor, the accuracy and reliability of barometric pressure measurement (clearance measurement) using operating parameters is not high. For this reason, by confirming the atmospheric pressure measurement by head-disk contact, head-disk contact in the subsequent read / write operation is avoided or a clearance margin is more reliably ensured. It is not preferable that the verification frequency of the head-disk contact is too high because the extra processing time of the HDD increases. Therefore, the HDD according to the present embodiment verifies the contact between the head and the disk when the atmospheric pressure change (clearance change) exceeds a preset threshold value.

  Before describing details of verification of TFC and head-disk contact of this embodiment, the overall configuration of the HDD will be described. FIG. 1 is a block diagram schematically showing the overall configuration of the HDD 1. The HDD 1 has a magnetic disk 11 that is a disk for storing data in the enclosure 10. The spindle motor (SPM) rotates the magnetic disk 11 at a predetermined angular velocity. Corresponding to each recording surface of the magnetic disk 11, a head slider 12 for accessing (reading or writing) the magnetic disk 11 is provided. Access is a superordinate concept of read and write. Each head slider 12 includes a slider that floats on the magnetic disk, and a head element unit that is fixed to the slider and converts between a magnetic signal and an electric signal.

  The head slider 12 of this embodiment includes a heater for TFC that expands and projects the head element portion by heat and adjusts the clearance (flying height) from the magnetic disk 11. The structure of the head slider 12 will be described in detail later with reference to FIG. Each head slider 12 is fixed to the tip of the actuator 16. The actuator 16 is connected to a voice coil motor (VCM) 15, and moves in the radial direction on the magnetic disk 11 that rotates the head slider 12 by rotating about a rotation axis. The actuator 16 and the VCM 15 are moving mechanisms for the head slider 12.

  Circuit elements are mounted on the circuit board 20 fixed to the outside of the enclosure 10. The motor driver unit 22 drives the SPM 14 and the VCM 15 according to control data from the HDC / MPU 23. The RAM 24 functions as a buffer that temporarily stores read data and write data. An arm electronic circuit (AE: Arm Electronics) 13 in the enclosure 10 selects the head slider 12 that accesses the magnetic disk 11 from among the plurality of head sliders 12, amplifies the reproduction signal, Send to the write channel (RW channel) 21. Further, the recording signal from the RW channel 21 is sent to the selected head slider 12. The AE 13 further functions as an adjustment circuit that supplies power to the heater of the selected head slider 12 and adjusts the amount of power.

  In the read process, the RW channel 21 amplifies the read signal supplied from the AE 13 so as to have a constant amplitude, extracts data from the acquired read signal, and performs a decoding process. The data to be read includes user data and servo data. The decoded read user data and servo data are supplied to the HDC / MPU 23. In the write process, the RW channel 21 code-modulates the write data supplied from the HDC / MPU 23, further converts the code-modulated write data into a write signal, and supplies the write signal to the AE 13.

  The HDC / MPU 23, which is an example of a controller, performs read / write processing control, command execution order management, positioning control (servo control) of the head slider 12 using servo signals, interface control with the host 51, and defect management. Necessary processing related to data processing such as error handling processing when an error occurs and overall control of the HDD 1 are executed. In particular, the HDC / MPU 23 of the present embodiment performs TFC according to the temperature according to the temperature detected by the temperature sensor 17, and further performs TFC according to the atmospheric pressure. Further, the HDC / MPU 23 verifies the contact between the head and the disk when the change in atmospheric pressure specified by the operation parameter is large. These points will be described later.

  FIG. 2 is a cross-sectional view showing a configuration in the vicinity of the air outflow end surface (trailing side end surface) 121 of the head slider 12. The slider 123 supports the head element unit 122. The head element unit 122 includes a read element 32 and a write element 31. The write element 31 generates a magnetic field between the magnetic poles 312 with a current flowing through the write coil 311 and writes magnetic data to the magnetic disk 11. The read element 32 includes a magnetoresistive element 32 a having magnetic anisotropy, and reads out magnetic data by a resistance value that changes due to a magnetic field from the magnetic disk 11.

  The head element portion 122 is formed on an AlTiC (AlTiC) substrate constituting the slider 123 by a thin film formation process. The magnetoresistive element 32 a is sandwiched between magnetic shields 33 a and 33 b, and the write coil 311 is surrounded by an insulating film 313. A protective film 34 such as alumina is formed around the write element 31 and the read element 32. A heater 124 exists in the vicinity of the write element 31 and the read element 32. The heater 124 can be formed by meandering a thin film resistor using permalloy or the like and filling the gap with alumina.

  When the AE 13 passes a current through the heater 124, the vicinity of the head element portion 122 is deformed by the heat of the heater 124. For example, when not heated, the ABS surface 35 of the head slider 12 has a shape indicated by S1, and a clearance, which is a distance between the head element portion 122 and the magnetic disk, is indicated by C1. The protruding shape S2 when the heater 124 is heated is indicated by a broken line. The head element portion 122 approaches the magnetic disk 11, and the clearance C2 at this time is smaller than the clearance C1. FIG. 2 is a conceptual diagram, and the dimensional relationship is not accurate. The protrusion amount and clearance of the head element portion 122 change according to the heater power value supplied to the heater 124.

In the following, the verification of the TFC and head / disk contact of this embodiment will be described in more detail. As described above, the HDC / MPU 23 of the present embodiment performs TFC according to temperature and atmospheric pressure. The heater power P applied to the heater 124 is represented by the sum (P (t) + P (p)) of the heater power P (t) depending on the temperature and the heater power P (p) depending on the atmospheric pressure. The It should be noted that the constant term is incorporated in any of the mathematical expressions, and the coefficient of each mathematical expression can be changed according to environmental conditions such as temperature and atmospheric pressure, the head slider 12 or the radial position thereof. Specifically, the heater power P is expressed by the following mathematical formula.
P = (TDP × eff [DEFAULT] −Target
−dt × t_comp−dp × p_comp) / eff

  eff is the heater power efficiency, and changes according to the atmospheric pressure and the radial position. eff [DEFAULT] is the heater power efficiency in the default condition. TDP is the heater power at which the head slider 12 and the magnetic disk 11 are in contact with each other under the default condition, Target is the target clearance, dt is the temperature change from the default condition, t_comp is the clearance change rate with respect to temperature, and dp is from the default condition P_comp is a clearance change rate with respect to the atmospheric pressure. The signs of t_comp and p_comp are opposite. TDP, t_comp, and p_comp typically vary with radial position. The default conditions are typically environmental conditions of 30 ° C. (room temperature) and 1 atmosphere (altitude 0 m).

  The HDC / MPU 23 controls the heater power P according to the temperature detected by the temperature sensor 17. Specifically, data indicating the relationship between the detected temperature and the heater power is set in the HDD 1, and the HDC / MPU 23 determines the heater power depending on the temperature according to the data and the detected temperature. The relationship between temperature and heater power depends on the head slider 12, the radial position (or zone) of the magnetic disk 11, and the atmospheric pressure.

  Since the HDD 1 of this embodiment does not have an atmospheric pressure sensor, it cannot directly measure the atmospheric pressure. Therefore, the HDC / MPU 23 performs TFC according to the atmospheric pressure by measuring the clearance. The clearance changes according to the atmospheric pressure. Therefore, the HDC / MPU 23 measures the clearance and specifies the atmospheric pressure change dp from the clearance change. Since the clearance also changes depending on the temperature, the HDC / MPU 23 can specify the clearance change due to the change in atmospheric pressure by correcting the clearance change due to the temperature change from the measured clearance. As described above, by defining a default condition having a specified default temperature and pressure and a default clearance in the default condition, a change in each value is associated with a current value.

  The temperature-corrected clearance change represents a change in atmospheric pressure. The HDC / MPU 23 controls the heater power P in accordance with the specified atmospheric pressure (atmospheric pressure change) due to the clearance change. Specifically, the HDD 1 is set with data representing the relationship between the atmospheric pressure change represented by the clearance change and the heater power, and the HDC / MPU 23 adjusts the atmospheric pressure according to the data and the measured atmospheric pressure. The heater power corresponding to it is determined.

  The HDD 1 of this embodiment specifies a clearance or a clearance change from the default clearance from the read signal of the head slider 12. More specifically, the clearance is specified from the resolution of the read signal (resolution of the frequency component). For example, the resolution can be expressed by a ratio of a specific low frequency signal to a high frequency signal in the read signal. There are several operating parameters to identify pressure changes or clearance changes due to pressure changes, among which the identification of clearance changes using resolution is one of the most accurate methods. . When the clearance is reduced, the amplitude of the high frequency component of the read signal is increased, and the signal resolution, that is, the resolution is increased.

  The resolution and the clearance are in a linear relationship, and the clearance can be expressed as a linear function of the resolution by applying an appropriate linear transformation to the resolution. Typically, the linear function that links the resolution and the clearance is different for each head slider 12. The relationship between the resolution of each head slider 12 and the clearance is specified in a test process in manufacturing the HDD 1, and control parameters corresponding to the relationship are registered in the HDD 1.

  The HDC / MPU 23 can specify the resolution by analyzing the read signal and calculating the ratio of the high frequency signal gain (amplitude) to the low frequency signal gain (amplitude). However, in order for the HDC / MPU 23 to perform the process, an additional function is required in addition to the function necessary for the normal operation. In addition, the MPU requires a lot of processing time to perform the processing. Therefore, it is preferable to measure the resolution using a function mounted on the HDD 1. The RW channel 21 has a function of adjusting the reproduction waveform of the read signal in order to accurately extract data from the read signal. The RW channel 21 performs this waveform shaping using a digital filter.

  A digital filter (adaptive cosine filter) that corrects a frequency component of a reproduction signal is known as a digital filter mounted on the RW channel 21. The RW channel 21 corrects the tap value of this filter from the measurement result of the read signal. This correction value has a linear relationship with the clearance (resolution) and is a value representing the resolution. This digital filter is an existing technology as disclosed in Japanese Patent Laid-Open No. 5-81807 and US Pat. No. 5,168,413, and will not be described in detail. The HDC / MPU 23 can specify the clearance change by referring to the correction value. Hereinafter, this correction value is referred to as Kgrad. In a test process in manufacturing, the relationship between Kgrad and clearance is specified for each head slider 12.

  In the following description, the HDC / MPU 23 specifies the clearance (clearance change) with reference to Kgrad, which is one of the channel parameters, but the HDC / MPU 23 uses other channel parameters representing the resolution. May be. For example, when the RW channel 21 has a digital filter for restoring the reproduction signal of the specific pattern to the reference pattern, the HDC / MPU 23 corrects the resolution component correction value in the correction coefficient of the tap of the digital filter. Can be used to identify clearance.

  As described above, the test process in manufacturing HDD1 specifies the relationship between heater power and clearance, the relationship between temperature and clearance, the relationship between temperature-corrected Kgrad and clearance, and sets data representing them in HDD1. sign up. Kgrad changes due to a temperature change in the characteristics of the RW channel 21 in addition to a clearance change due to a temperature change. The Kgrad temperature correction is performed by combining these changes. By using these setting data, the HDC / MPU 23 can determine an appropriate heater power value from the detected temperature of the temperature sensor 17 and the measured value of Kgrad.

  The HDC / MPU 23 can acquire Kgrad from the RW channel 21 at an arbitrary timing. However, unlike temperature, the air pressure does not change significantly during operation, and typically the air pressure after startup is constant. Therefore, the HDC / MPU 23 of this embodiment controls the heater power according to the temperature change after startup, but the atmospheric pressure (Kgrad) is measured in the initial setting process (power-on-reset (POR) process) at startup. The TFC is performed on the assumption that the atmospheric pressure during operation is the same as the atmospheric pressure during startup. The HDC / MPU 23 may measure the atmospheric pressure during the operation after POR and control the heater power according to the change.

  A characteristic point of this embodiment is that the head-disk contact is verified when the measured change in atmospheric pressure is large. As described above, the HDC / MPU 23 specifies a change in air pressure (representing a change in clearance) from the Kgrad and the temperature detected by the temperature sensor 17 in the POR process. If the change in air pressure from the default air pressure is not within the standard, the HDC / MPU 23 verifies the head / disk contact. Measurement of changes in atmospheric pressure with Kgrad is not as accurate and stable as sensors. For this reason, when the change in Kgrad is large, the reliability of the subsequent read / write operation can be improved by verifying the measurement result. In particular, when the atmospheric pressure is measured only in the POR, the margin for the subsequent atmospheric pressure change is important. Further, by verifying the head-disk contact when the change in atmospheric pressure exceeds the reference, it is possible to avoid an excessive increase in processing time for verification.

  FIG. 3A is a diagram schematically showing the relationship between the measurement result of altitude change (atmospheric pressure change) and verification of head-disk contact. As the altitude increases, the air pressure decreases. FIG. 3A shows an altitude, a measured value of Kgrad, a default Kgrad, and a reference range K_criteria for determining whether or not to verify head / disk contact. Kgrad shown is a temperature-corrected value. As described above, the default Kgrad is a value specified in the test process (TEST). As illustrated in FIG. 3A, Kgrad does not completely follow altitude (atmospheric pressure).

  In the first three PORs, the altitude and measured Kgrad are within the reference range K_criteria. Therefore, the HDC / MPU 23 does not verify the head / disk contact. In the fourth POR, the altitude A and the measured Kgrad exceed the reference range K_criteria. The HDC / MPU 23 verifies the head-disk contact in this POR. Thereafter, in the fifth POR, the altitude A and the measured Kgrad are within the reference range K_criteria. Therefore, the HDC / MPU 23 does not verify the head / disk contact.

  As shown in FIG. 3A, the reference range K_criteria preferably has threshold values above and below the default Kgrad. This is because a typical default altitude is 0 m above sea level, but in an actual use environment, it may be in a pressurized environment or may be 0 m or less. However, head-disk contact may be verified only by design if the altitude rises above a threshold.

  With reference to the flowchart of FIG. 4 and the block diagram of FIG. 5, the flow of atmospheric pressure measurement and head-disk contact verification in this embodiment will be described. The HDC / MPU 23 performs atmospheric pressure measurement in the POR process. First, the HDC / MPU 23 measures Kgrad at the heater power 0 (S11). Specifically, the HDC / MPU 23 selects one head slider 12 and controls the VCM 15 via the motor driver 22 to move the head slider 12 to a predetermined data track.

  The head slider 12 reads access destination data under the control of the HDC / MPU 23. The RW channel 21 calculates Kgrad from the read signal of the head slider 12 and stores it in a register in the RW channel 21. The HDC / MPU 23 accesses the register of the RW channel 21 and acquires Kgrad. Preferably, Kgrad is measured a plurality of times, and a value for specifying the clearance is calculated from the plurality of measured values. In a preferred example, the HDC / MPU 23 uses an average value of a plurality of measured values. Even under the same environment (atmospheric pressure and temperature), the Kgrad measurement value varies from measurement to measurement, so it is more accurate to specify the clearance from multiple measurement results. is there.

  The data track used for Kgrad measurement is preferably a data track having excellent characteristics for Kgrad measurement. For this reason, it is preferable to be in an area that is not used for recording user data and is not accessed from the host 51. Thereby, it is possible to avoid the deterioration of the characteristics of the data track due to repeated overwriting. Further, in an HDD having a ramp outside the magnetic disk 11, it is preferable that the HDD be on the inner peripheral side than the innermost peripheral end of the user area. This is because the head slider 12 does not pass through this region in normal operation.

  Next, the HDC / MPU 23 specifies a clearance from Kgrad (S12). Specifically, the amount of clearance change from the default clearance is specified from the difference between the default Kgrad and the measured Kgrad under default conditions (for example, 30 ° C. and 1 atm). The clearance change amount can be expressed by, for example, a heater power value. The default Kgrad is a temperature-corrected value, and the HDC / MPU 23 similarly corrects the temperature of the Kgrad measurement value according to the detected temperature. By comparing the temperature-corrected default Kgrad and the measured value, the HDC / MPU 23 can specify a change in atmospheric pressure from the default atmospheric pressure (for example, 1 atmospheric pressure) from the Kgrad.

  FIG. 6 schematically shows the relationship between Kgrad, clearance, heater power, and atmospheric pressure (altitude). Kgrad is a value after temperature correction. As shown in FIG. 6, the above values have a linear relationship with each other. Therefore, the HDC / MPU 23 can directly specify another value from any of the above values, and one value can represent another value.

  In the above process, Kgrad at heater power 0 is measured and the value is corrected by the detected temperature. However, the Kgrad may be measured in a state where the heater power value corresponding to the default setting of TFC, the detected temperature, and the radial position is given to the heater 124. A value obtained by correcting the temperature change of the channel characteristic with respect to the measured Kgrad shows a change in Kgrad corresponding to the change in atmospheric pressure. Thus, the temperature correction of Kgrad can be performed by calculation alone or by adjusting the clearance by TFC.

  Next, the HDC / MPU 23 determines whether or not the clearance change specified from Kgrad is within the reference range (S13). The clearance change is expressed by, for example, heater power, nanometer, or Kgrad. The HDC / MPU 23 compares the measured clearance change with the threshold of the reference range, and if the clearance change is within the reference range (Y in S13), records the measurement result without verifying head-disk contact. In step S16, the atmospheric pressure measurement process is terminated.

  If the measured clearance change exceeds the reference range (N in S13), the HDC / MPU 23 verifies the head-disk contact (S14). The head-disk contact verification process of this embodiment will be described with reference to the flowchart of FIG. The HDC / MPU 23 determines the heater power value in the read / write operation according to the default setting of TFC from the detected temperature of the temperature sensor 17 and the measured Kgrad (S141). The HDC / MPU 23 determines a default heater power value corresponding to the detected temperature and Kgrad from control data such as functions and tables that are set and registered in advance.

  The HDC / MPU 23 verifies the head-disk contact at a heater power value larger than the default heater power value (S142). FIG. 8A schematically shows the head slider 12 at the default heater power Pa, and FIG. 8B shows the head slider 12 at the heater power value Pb for verification of head-disk contact. Is schematically shown. In the verification of the head-disk contact, the head element part 122 protrudes from the default state (Pb> Pa), and the clearance Cb is smaller than the default clearance Ca (Cb <Ca). By checking whether contact is detected in a state where the clearance is smaller than the default state, it is possible to appropriately specify whether the necessary clear run margin is present.

  First, the HDC / MPU 23 moves the head slider 16 (or another head slider 12) selected for measuring Kgrad to a predetermined data track by controlling the actuator 16. The HDC / MPU 23 stores data representing a heater power value larger than the heater power value set to the default TFC in the AE 13 register. The AE 13 supplies the heater power corresponding to the data to the head slider 12. The HDC / MPU 23 controls the AE 13 and accesses a predetermined data sector by the head slider 12. Access may be either read or write, but typically, the HDC / MPU 23 reads a predetermined data sector. The data sector that uses head disk contact for verification is preferably an area that the host 51 does not access. This is because, if contact detection is performed in an area that is not a storage area for user data or servo data accessed by the host, it is possible to prevent the data area from being damaged.

  When the contact between the head slider 12 and the magnetic disk 11 is not detected (N in S143), the HDC / MPU 23 completes the verification of the head disk contact without correcting the default heater power setting value. To do. Several methods for detecting head-disk contact are known. For example, the HDC / MPU 23 can detect head-disk contact by measuring the amplitude of the read signal, the VCM current value, or the SPM current value. When contact between the head slider 12 and the magnetic disk 11 is detected (Y in S143), the HDC / MPU 23 makes the heater power setting value in the read / write operation smaller than the default setting value (S144). FIG. 8C schematically shows the head slider 12 at a heater power value Pc smaller than the default setting value Pa. Under the same environment and operating conditions, the corrected heater power value Pc is smaller than the default heater power value Pa, and the corrected clearance Cc is larger than the default clearance Ca.

  In a preferred example, the heater power decrease amount from the default value is the same as the heater power increase amount in the contact verification. This efficient process verifies that the required clearance margin exists, and at the same time ensures that the required clearance margin is secured by correcting the heater power value if the required margin does not exist. it can. Since the HDD 1 of this example performs atmospheric pressure measurement only at the time of start-up, the heater power value in the subsequent read / write operation is smaller than the preset default setting by the heater power reduction amount at each temperature.

  As described above, it is preferable to verify head-disk contact at a constant clearance. Although it is possible to verify the head-disk contact by changing the clearance, this increases the processing time for verification. In order to shorten the processing time, it is preferable to verify the head-disk contact only at a specific clearance. In addition, sufficient reliability can be achieved even when only one clearance is verified.

  When the head-disk contact verification (S14) is completed, the HDC / MPU 23 performs a reference range update process (S15) for determining whether to verify the head-disk contact (S13). When the HDD 1 is always used at high altitude (low pressure), verification of head-disk contact is performed at every POR. This significantly increases the POR processing time. Further, as described above, if the head-disk contact verification is performed with a clearance smaller than the clearance according to the default TFC setting, the possibility of contact increases, so that damage to the head slider 12 may also increase. . By updating the reference range, it is possible to reduce the number of necessary contact verifications according to the usage environment of the HDD 1.

  This update process will be described with reference to the flowchart of FIG. As shown in the flowchart of FIG. 4, the HDC / MPU 23 records the measurement result of the atmospheric pressure change (clearance change) due to Kgrad (S16). The HDC / MPU 23 refers to the past measurement results and updates the reference range when the number of times the pressure drop (clearance reduction) exceeds the reference range reaches a predetermined number (Y in S151) (S152). If the predetermined number has not been reached (N in S151), the HDC / MPU 23 does not update the reference range.

  In a preferred example, the HDC / MPU 23 updates the reference range when the number of times exceeding the reference range has reached N times in the closest past M PORs. M and N are selected as appropriate natural numbers by design, and these may be the same value. As a reference range update method, for example, only the default Kgrad is updated. The value from the default Kgrad to the boundary of the reference range is the same. Alternatively, both the default Kgrad and the reference range boundary may be updated.

  FIG. 3B is a diagram schematically showing the relationship between the measurement result of altitude change (atmospheric pressure change), head-disk contact verification, and update of the reference range. The meaning of the symbols is the same as in FIG. In the example of FIG. 3B, when the Kgrad exceeds the reference range in the last three consecutive PORs, the HDC / MPU 23 updates the default Kgrad to the current Kgrad measurement value. In FIG. 3B, the HDC / MPU 23 updates the default Kgrad at the fifth POR. In this example, the reference range is updated only once.

  In the subsequent POR, the HDC / MPU 23 determines the presence or absence of contact verification based on the updated reference range. The Kgrad measurement values at the 8th and 9th PORs are close to the default altitude in the test process, but the reference range has already been updated, so the HDC / MPU 23 verifies the head-disk contact.

  As mentioned above, although this invention was demonstrated taking preferable embodiment as an example, this invention is not limited to said embodiment. A person skilled in the art can easily change, add, and convert each element of the above-described embodiment within the scope of the present invention. The present invention can be applied to a disk drive apparatus having a clearance adjustment mechanism other than TFC such as a piezo element. As described above, it is preferable to measure the change in atmospheric pressure using a read signal, particularly resolution, but other operational parameters such as SPM current may be used to measure the atmospheric pressure change. The HDC / MPU 23 may verify the head-disk contact at a timing other than POR. The measurement position of Kgrad can be performed at any radial position on the recording surface. The present invention may be applied to an HDD on which a head slider having only a read element is mounted, or to a disk drive device other than the HDD.

In this embodiment, it is a block diagram which shows typically the whole structure of HDD. In this embodiment, it is sectional drawing which shows typically the structure of the head slider provided with the heater for TFC. In this embodiment, it is a figure which shows typically the relationship of the reference | standard range which determines the measurement result of an altitude change (atmospheric pressure change), verification of head-disk contact, and the implementation of verification. In this embodiment, it is a flowchart which shows the flow of verification of an atmospheric pressure measurement and a head disk contact. In this embodiment, it is a block diagram which shows the logic component which performs a barometric pressure measurement and verification of a head disk contact. In this embodiment, it is a figure which shows typically the relationship between Kgrad, clearance, heater power, and atmospheric pressure (altitude). In this embodiment, it is a flowchart which shows the flow of a verification process of a head disk contact. In this embodiment, it is a figure which shows typically the head slider in a normal process after performing the head slider in a normal process, the head slider in a contact verification process, and heater setting correction | amendment. 5 is a flowchart showing a flow of reference range update processing for determining whether or not to verify head-disk contact in the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hard disk drive, 10 Enclosure, 11 Magnetic disk 12 Head slider, 14 Spindle motor, 15 Voice coil motor 16 Actuator, 20 Circuit board, 21 Read / write channel 22 Motor driver unit, 23 Hard disk drive Controller / MPU
24 RAM, 31 Write element, 32 Read element, 32a Magnetoresistive element 33a, b Shield, 34 Protective film, 51 Host, 121 Trailing side end face 122 Head element part, 123 Slider, 124 Heater, 311 Write coil 312 Magnetic pole, 313 Insulating film

Claims (16)

A head to access the disk;
A moving mechanism for holding the head and moving the head on the disk;
An adjustment mechanism for adjusting the clearance between the head and the disk;
A temperature sensor;
A controller for controlling at least the adjusting mechanism;
Have
The controller is
After correcting the change amount due to the temperature change in the change amount from the default value of the operation parameter specified from the read signal read from the disk by the head using the detected temperature of the temperature sensor, the corrected operation parameter Determine the amount of clearance change by the amount of change,
Only when the clearance change amount exceeds the reference range, verify the contact between the head and the disk,
Based on the result of the contact verification, determine the adjustment amount of the clearance,
Measuring the change of the operation parameter a plurality of times, and determining whether the clearance change amount exceeds the reference range based on the measurement result of the plurality of times;
Disk drive device. The operating parameter is a parameter determined from the amplitude of a read signal read from the disk by the head.
The disk drive device according to claim 1. The operation parameter is a parameter determined from a ratio of different frequency components of a read signal read from the disk by the head.
The disk drive device according to claim 1. The controller controls the adjustment mechanism so that a clearance when verifying the contact is smaller than a default clearance corresponding to the determined amount of change in the clearance;
The disk drive device according to claim 1. The controller verifies the contact at a constant adjustment clearance amount by the adjustment mechanism.
The disk drive apparatus according to claim 4. Wherein the controller, when confirming the contact in the verification of the contact, to control the adjustment mechanism such clearance is higher than the default setting of the clearance corresponding to the determined said clearance changed amount,
The disk drive device according to claim 1. Wherein the controller has confirmed the contact in the verification of the contact, the higher the clearance than the default setting of the clearance amount higher than the default setting the clearance, the default setting the clearance in the verification of the contact Controlling the adjustment mechanism to be equal to the amount to be smaller than,
The disk drive apparatus according to claim 4. The controller changes the reference of the clearance change amount for determining whether or not to perform the contact verification based on the number of times the clearance change amount exceeds the reference range.
The disk drive device according to claim 1. A clearance adjustment method in a disk drive device,
The temperature is detected by the temperature sensor,
After correcting the change amount due to the temperature change in the change amount from the default value of the operation parameter specified by the read signal read from the disk by the head that accesses the disk, using the detected temperature, the corrected operation parameter The amount of clearance change is determined by the amount of change,
Only when the clearance change amount exceeds the reference range, verify the contact between the head and the disk,
Based on the result of the contact verification, determine the adjustment amount of the clearance,
Measuring the change of the operation parameter a plurality of times, and determining whether the clearance change amount exceeds the reference range based on the measurement result of the plurality of times;
Method. The operating parameter is a parameter determined from the amplitude of a read signal read from the disk by the head.
The method of claim 9. The operation parameter is a parameter determined from a ratio of different frequency components of a read signal read from the disk by the head.
The method of claim 9. The clearance when verifying the contact is made smaller than the default clearance corresponding to the determined amount of change in the clearance,
The method of claim 9. Verifying the contact at the fixed clearance amount;
The method of claim 12. When the contact is confirmed in the verification of the contact, the clearance is set higher than the default clearance corresponding to the determined clearance change amount .
The method of claim 9. Check out contact in the verification, a higher clearance than the clearance of the default settings,
The amount that makes the clearance higher than the default setting is the same as the amount that makes the clearance smaller than the default setting in the contact verification.
The method of claim 12. Changing the reference range of the clearance change amount for determining whether to perform the contact verification based on the number of times the clearance change amount exceeds the reference range;
The method of claim 9.

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